With increased demand for rapid execution of gene sequencing in diagnostic and forensic areas, the need for label free detection and identification of alleles is growing. Label-free sensors circumvent the need for fluorescence modifications, and they are based on, e.g., detecting plasmon resonance, electrochemical conductance, mechanical resonance, micro cavity resonance or evanescent field-based absorption or direct absorption. However, these techniques may have disadvantages in terms of limited sensitivity or specificity or signal to noise (caused by sensor structure defects) because they all depend on properties of materials external to nuclei acids. Thus, there is need for a sensor that only utilizes property(ies) unique to the DNA molecule.